Has anyone thought of doing one of the following?
1. Remove the heat shield/spreader and replace it with a piece of copper cut to the same shape, (I gather that you will need both thermal paste and epoxy to do this job.)
2. run the board outside of its case like a pc using a probe to see whats really going on (I noticed some people on the net ak Youtube claim that the 1st gen PS3 PSu's were faulty and pumped out more heat then the mobo.)
The heat blowing out of the back is more likely to be going through the motherboard and not directly through the heatsink.
Hope this helps... if alll else fails try liquid cooling xD